Sensor unit

1. A sensor unit comprising: a substrate; a plurality of light receiving parts arranged on the substrate and for detecting light; and one or more diffraction grating layers arranged over the substrate and the light receiving parts, the diffraction grating layers having two or more diffraction units, each of which diffracts light of a corresponding wavelength and thereby condenses the light at a corresponding one of the light receiving parts, wherein: at least two of the diffraction units are each constituted by a hologram formed in a first one of the diffraction grating layers; and at least some of the plurality of holograms formed in the first diffraction grating layer each overlap at least partly with some of the plurality of neighboring holograms.

2. The sensor unit according to claim 1 , wherein: at least one of the diffraction units is formed in a second one of the diffraction grating layers provided on the first diffraction grating layer; and at least some of the plurality of holograms formed in the first diffraction grating layer each overlap, in the plan view, at least partly with some of the diffraction units formed in the second diffraction grating layer.

3. The sensor unit according to claim 2 , wherein at least one of the diffraction units is constituted by a hologram or a convex-concave part.

4. The sensor unit according to claim 2 , wherein the hologram is formed of a material into which intensity distribution of incident light is recorded in the form of refractive index distribution.

5. The sensor unit according to claim 2 , wherein: the plurality of light receiving parts include light receiving parts for detecting light of different wavelengths, and are divided into a plurality of groups according to the wavelength of light to be detected; and for a group of light receiving parts having lower sensitivity to light of the target wavelength for their detection, a larger number of diffraction units corresponding to the light receiving parts are provided.

6. The sensor unit according to claim 2 , wherein: the plurality of light receiving parts include light receiving parts for detecting light of different wavelengths, and are divided into a plurality of groups according to the wavelength of light to be detected; and the plurality of light receiving parts are arranged such that, for a group of light receiving parts having lower sensitivity to light of the target wavelength for their detection, the total sum of center-to-center spacings, in the lateral direction perpendicular to the thickness direction of the substrate, between diffraction units corresponding to the light receiving parts is larger.

7. The sensor unit according to claim 1 , wherein at least one of the diffraction units is constituted by a hologram or a convex-concave part.

8. The sensor unit according to claim 7 , wherein the hologram is formed of a material into which intensity distribution of incident light is recorded in the form of refractive index distribution.

9. The sensor unit according to claim 7 , wherein: the plurality of light receiving parts include light receiving parts for detecting light of different wavelengths, and are divided into a plurality of groups according to the wavelength of light to be detected; and for a group of light receiving parts having lower sensitivity to light of the target wavelength for their detection, a larger number of diffraction units corresponding to the light receiving parts are provided.

10. The sensor unit according to claim 7 , wherein: the plurality of light receiving parts include light receiving parts for detecting light of different wavelengths, and are divided into a plurality of groups according to the wavelength of light to be detected; and the plurality of light receiving parts are arranged such that, for a group of light receiving parts having lower sensitivity to light of the target wavelength for their detection, the total sum of center-to-center spacings, in the lateral direction perpendicular to the thickness direction of the substrate, between diffraction units corresponding to the light receiving parts is larger.

11. The sensor unit according to claim 1 , wherein the hologram is formed of a material into which intensity distribution of incident light is recorded in the form of refractive index distribution.

12. The sensor unit according to claim 11 , wherein: the plurality of light receiving parts include light receiving parts for detecting light of different wavelengths, and are divided into a plurality of groups according to the wavelength of light to be detected; and for a group of light receiving parts having lower sensitivity to light of the target wavelength for their detection, a larger number of diffraction units corresponding to the light receiving parts are provided.

13. The sensor unit according to claim 11 , wherein: the plurality of light receiving parts include light receiving parts for detecting light of different wavelengths, and are divided into a plurality of groups according to the wavelength of light to be detected; and the plurality of light receiving parts are arranged such that, for a group of light receiving parts having lower sensitivity to light of the target wavelength for their detection, the total sum of center-to-center spacings, in the lateral direction perpendicular to the thickness direction of the substrate, between diffraction units corresponding to the light receiving parts is larger.

14. The sensor unit according to claim 1 , wherein: the plurality of light receiving parts include light receiving parts for detecting light of different wavelengths, and are divided into a plurality of groups according to the wavelength of light to be detected; and for a group of light receiving parts having lower sensitivity to light of the target wavelength for their detection, a larger number of diffraction units corresponding to the light receiving parts are provided.

15. The sensor unit according to claim 1 , wherein: the plurality of light receiving parts include light receiving parts for detecting light of different wavelengths, and are divided into a plurality of groups according to the wavelength of light to be detected; and the plurality of light receiving parts are arranged such that, for a group of light receiving parts having lower sensitivity to light of the target wavelength for their detection, the total sum of center-to-center spacings, in the lateral direction perpendicular to the thickness direction of the substrate, between diffraction units corresponding to the light receiving parts is larger.

16. The sensor unit according to claim 1 , further comprising an optical system for condensing incident light, on the opposite side to the substrate and the light receiving parts across the diffraction grating layers.

17. The sensor unit according to claim 1 , further comprising a filter for cutting off light of other wavelengths than a specific wavelength, on the light receiving parts.

18. The sensor unit according to claim 1 , further comprising an optical system for condensing incident light, between the diffraction units and the light receiving parts.

19. The sensor unit according to claim 1 , wherein the light receiving parts are made of a lead zirconate titanate family ceramic material.